snap remove lxd apparently deletes external zfs zpool but the disk is not re-usuable

[tomponline]

Problem: The zpool created by LXD on an external disk apparently get removed on snap remove, but not sufficiently for the disk to be reused for a fresh ZFS pool.

Fresh ubuntu 24.04 system with an empty external disk /dev/sdb:

lsblk
NAME    MAJ:MIN RM  SIZE RO TYPE MOUNTPOINTS
loop0     7:0    0 74.2M  1 loop /snap/core22/1380
loop2     7:2    0 38.8M  1 loop /snap/snapd/21759
sda       8:0    0   10G  0 disk 
├─sda1    8:1    0    9G  0 part /
├─sda14   8:14   0    4M  0 part 
├─sda15   8:15   0  106M  0 part /boot/efi
└─sda16 259:0    0  913M  0 part /boot
sdb       8:16   0   10G  0 disk 

Install LXD and create ZFS pool on /dev/sdb

snap install lxd
lxd (5.21/stable) 5.21.2-34459c8 from Canonical✓ installed
lxc storage create local zfs source=/dev/sdb

Install ZFS tools and inspect the newly create zpool:

apt install zfsutils-linux
zpool list
NAME    SIZE  ALLOC   FREE  CKPOINT  EXPANDSZ   FRAG    CAP  DEDUP    HEALTH  ALTROOT
local  9.50G   622K  9.50G        -         -     0%     0%  1.00x    ONLINE  -

zpool status
  pool: local
 state: ONLINE
config:

	NAME        STATE     READ WRITE CKSUM
	local       ONLINE       0     0     0
	  sdb       ONLINE       0     0     0

errors: No known data errors

Remove LXD and see that the partitions are left behind on /dev/sdb but the zpool has apparently gone:

snap remove lxd --purge

lsblk
NAME    MAJ:MIN RM  SIZE RO TYPE MOUNTPOINTS
loop0     7:0    0 74.2M  1 loop /snap/core22/1380
loop2     7:2    0 38.8M  1 loop /snap/snapd/21759
sda       8:0    0   10G  0 disk 
├─sda1    8:1    0    9G  0 part /
├─sda14   8:14   0    4M  0 part 
├─sda15   8:15   0  106M  0 part /boot/efi
└─sda16 259:0    0  913M  0 part /boot
sdb       8:16   0   10G  0 disk 
├─sdb1    8:17   0   10G  0 part 
└─sdb9    8:25   0    8M  0 part 

zpool status
no pools available

Install LXD again and try to create ZFS storage pool on /dev/sdb. See it fail due to left over ZFS pool export to "local" zpool:

snap install lxd
lxd (5.21/stable) 5.21.2-34459c8 from Canonical✓ installed
lxc storage create local zfs source=/dev/sdb
Error: Failed to run: zpool create -m none -O compression=on local /dev/sdb: exit status 1 (invalid vdev specification
use '-f' to override the following errors:
/dev/sdb1 is part of exported pool 'local')

Manually wipe partitions on /dev/sdb and see that LXD can create new ZFS pool successfully on /dev/sdb:

fdisk /dev/sdb

Welcome to fdisk (util-linux 2.39.3).
Changes will remain in memory only, until you decide to write them.
Be careful before using the write command.


Command (m for help): d
Partition number (1,9, default 9): 1

Partition 1 has been deleted.

Command (m for help): d
Selected partition 9
Partition 9 has been deleted.
Command (m for help): w
The partition table has been altered.
Calling ioctl() to re-read partition table.
Syncing disks.


lxc storage create local zfs source=/dev/sdb
Storage pool local created